How Long Does Plan B Stay In Your System?

Unprotected sex is never a good idea. It not only leaves you open to getting pregnant but can also leave you defenseless against sexually transmitted infections. If you’ve had unprotected sex and are looking to prevent an unwanted pregnancy, there is emergency contraception available over the counter without a prescription. Plan B is the most widely available one. Here, you’ll find more information about the contraceptive including an answer to your question “how long does Plan B stay in your system?” Make sure you keep all of this information in mind before taking Plan B.


What Is Plan B?

Plan B is the brand name of an over-the-counter birth control that is made to work after having unprotected sex. It was made in the 1960s and was created to stop fertilization by changing the way sperm and the ova move in the body. It has been used since the 1980s as a contraceptive but has recently come into popularity with around 11 percent of sexually active women in the US choosing to use Plan B. If you’re one of the women who has already taken Plan B or if you’re considering taking it, you should first learn about the pill.

Before you take Plan B, it’s important to know what to expect. Like some birth control medications, some women feel nauseous and may even vomit after taking the pill. You may also experience some spotting in the few days after taking Plan B. Your regular menstruation cycle, however, should remain unaffected. It is recommended that you refrain from having sex until you complete your next menstruation cycle, but if you do decide to have sex, you should take care to use protection (preferably a male or female condom instead of a hormone-related contraceptive).

The recommended dose for Plan B is a single tablet as soon as possible following unprotected sex (no more than 72 hours after unprotected sex). The sooner you take the pill, the better it will work. The only real way to know that Plan B worked is when you begin your next menstrual cycle. If you don’t get your period within a week of your expected start date, you may be pregnant and should see your doctor.

Plan B should work as stated but there are some factors that can hinder its effectiveness. Some of these factors are:

  • You vomit within the first two hours after taking the medication
  • You had unprotected previously within the same menstrual cycle
  • You had a failed birth control method within the same menstrual cycle
  • You’ve already taken Plan B once during the same menstrual cycle

In addition, there are also side effects that can be expected, just as there are with any medication you may take. Some of the commonly reported side effects of Plan B are:

  • Nausea/vomiting
  • Lower abdominal pain/cramps
  • Fatigue
  • Dizziness
  • Menstruation issues (lighter or heavier than usual, slightly late or early start)

There are also rare side effects that include depression, hair loss, and blood clots. These side effects should go away as Plan B leaves your system but if you are still experiencing side effects after a few days, see your doctor. This leads back to the question, how long does Plan B stay in your system?

How Long Does Plan B Stay In Your System?

The best way to determine how long any medication stays in your system is to examine its half-life. This is the amount of time it takes for half of the medication to clear out of your system. The half-life of Plan B is reported to be around 24 hours. Research does show, however, that there can be a deviation of about five hours more or less than the 24-hour estimated half-life of the emergency contraceptive. This is an average, of course. More thorough research estimated the half-life of the medication to be closer to 28-36 hours with a six to 13-hour deviation (+/-).

Based on these calculations, it can be concluded that Plan B can take as little as 72 hours to pass through your system and as long as a full two weeks if your body metabolizes medications slower than the average time. For people with normal rates, Plan B should be eliminated from your body within a week of taking the medication.

There are different variables that can affect how long the medication stays in your body, however. These influences are:

  • The dosage taken: if you take a higher dose, it will stay in your system longer as the half-life of the medication will be increased.
  • How often the medication is used: if you take Plan B too often, your body (bodily tissue, specifically) will be saturated with the levonorgestrel (the main ingredient) and will, therefore, take a longer time to process and eliminate it from your body. The opposite is also true; if you rarely take Plan B, you may metabolize it faster than the average time.
  • An individual’s health/attributes: individual factors like your weight, genetics, and age may affect how fast or slow Plan B leaves your body. This is especially true when it comes to weight since Plan B is believed to be soluble in fat. Therefore, obese/overweight women may experience a higher accumulation of the medication in their body and take longer than normal to metabolize it. Metabolic rate is also an individual element that can influence how long it takes to eliminate a medication from your system.
  • Hepatic function: the health of your liver also has an influence on how long Plan B stays in your system. If you have cirrhosis or a similar hepatic impairment, the way your liver metabolizes medications is skewed so elimination may take longer. Usually, the degree of your liver’s impairment is parallel to the elimination time. For example, if you have a severe impairment it will take you a significantly longer time to clear Plan B while a minor impairment will take only slightly longer than usual. Renal function will also have an influence on the elimination time of Plan B for similar reasons.
  • Other medications in use: if you are taking any other medications or are abusing other drugs, it can take Plan B longer to get out of your system because your metabolic rate and hepatic function might be compromised from having to process so many different medications. This is because the isoenzymes that would be responsible for breaking down Plan B may be dealing with interference from other medications.


Hopefully, the information here has taught you more about emergency contraception and has answered your question “how long does Plan B stay in your system?” Remember, the information here is general and based on averages. There are certain factors that may increase or decrease the time it takes for your body to eliminate the contraceptive. If you’re concerned about your health or are experiencing prolonged side effects that you believe are from Plan B, visit your doctor and talk to him or her about what you’re experiencing.

Anna Smith

Hi there ! I’m Anna Smith, chief editor at Healthankering. I'm a proud mother of three passionate about health tips, beauty and ways to live healthier with more energy ! We start Healthankering to provide advanced material about not only the best ways to get healthy, but also to entertain and create a great community. Welcome aboard !

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